1. Field of the Invention
The present invention involves enhancing the conductivity of subterranean propped fractures penetrating formations while controlling proppant flowback. More particularly, the present invention relates to improved consolidation performance of resin-coated proppants and their use in controlling proppant flowback.
2. Description of Related Art
A subterranean formation may be treated to increase its conductivity by hydraulically fracturing the formation to create or enhance one or more cracks or “fractures.” Such hydraulic fracturing is usually accomplished by injecting a viscous fracturing fluid into the subterranean formation at a rate and pressure sufficient to cause the formation to break down and produce one or more fractures. The fracture or fractures may be horizontal or vertical, with the latter usually predominating, and with the tendency toward vertical fractures increasing with the depth of the formation being fractured. The fracturing fluid is generally a highly viscous gel, emulsion, or foam that may comprise a particulate material often referred to as proppant. In some fracturing operations, commonly known as “water fracturing” operations, the fracturing fluid viscosity is somewhat lowered and yet the proppant remains in suspension because the fracturing fluid is injected into the formation at a substantially higher velocity. Whether a highly viscous fluid is used or a less viscous fluid with a higher velocity, proppant is deposited in the fracture and functions, inter alia, to hold the fracture open while maintaining conductive channels through which produced fluids can flow upon completion of the fracturing treatment and release of the attendant hydraulic pressure.
In order to prevent the subsequent flowback of proppant and other unconsolidated particulates with the produced fluids a portion of the proppant introduced into the fractures may be coated with a hardenable resin composition. When the fracturing fluid, which is the carrier fluid for the proppant, reverts to a thin fluid the resin-coated proppant is deposited in the fracture, and the fracture closes or partially closes on the proppant. Such fractures apply pressure on the resin-coated proppant particles, causing the particles to be forced into contact with each other while the resin composition hardens. The hardening of the resin composition under pressure brings about the consolidation of the resin-coated proppant particles into a hard permeable mass having compressive and tensile strength that hopefully prevents unconsolidated proppant and formation sand from flowing out of the fractures with produced fluids. Flowback of the proppant or formation fines with formation fluids is undesirable as it may erode metal equipment, plug piping and vessels, and cause damage to valves, instruments, and other production equipment, and ultimately reduce the potential production of the well.
Most of the resin on resin pre-coated proppant is already cured. This partially cured resin needs to be softened either by temperature or an activator (as in the case of low temperature wells) so that the resin can be wedged together as the resin coated proppant grains contact one another. In addition to the softening effect of resin coated on the proppant, closure stress is required to cause grain-to-grain contact. Without grain-to-grain contact, adequate consolidation of proppant pack generally will not occur.